In recent years, moving-object recognition apparatuses have been developed, which recognize a speed and a change in movement of a moving object such as a vehicle traveling ahead of a user's vehicle or a pedestrian, detect a dangerous situation in its early stage, and notify a driver thereof so as to avoid the danger. Examples of the dangerous situation include sudden braking of the vehicle traveling ahead, another car coming in between the user's vehicle and the vehicle traveling ahead, and a pedestrian running into the road.
For example, there is a method that includes, for recognition of a moving object in front, obtaining changes in distance to the object in front by using changes in size of the object between image frames of two-dimensional images and the focal distance of a camera. However, one disadvantage is that, with this method, the measurement accuracy of this method for the distance to an object, more specifically, for example, the detection accuracy for changes in movement of a moving object is low.
To address this disadvantage, Patent Literature 1 (Japanese Laid-open Patent Publication No. 2000-266539) discloses an inter-vehicle distance measuring apparatus that obtains parallax images (also called distance images) by calculating parallax from stereo images obtained by a stereo camera apparatus. Note that a parallax image refers to an image obtained by converting parallax into brightness.
This inter-vehicle distance measuring apparatus disclosed in Patent Literature 1 cited herein detects a vehicle in front by using parallax images, and measures the distance between the vehicles and changes in the distance by using the size and direction of a motion vector of an edge of the detected vehicle.
However, the inter-vehicle distance measuring apparatus disclosed in Patent Literature 1 has the inconvenience that it recognizes moving objects directly from a parallax image obtained by a stereo camera apparatus and therefore provides low accuracy in moving-object recognition.